This invention relates, in general, to interruption processing within a computing environment, and in particular, to handling interruptions generated by adapters of the computing environment.
Message signaled interruption (MSI) is a way for an adapter function, such as a Peripheral Component Interconnect (PCI) function, to generate a central processing unit (CPU) interruption to notify the operating system of the occurrence of an event or the presence of some status. MSI is an alternative to having a dedicated interruption pin on each device. When an adapter function is configured to use MSI, the function requests an interruption by performing an MSI write operation of a specified number of bytes of data to a special address. The combination of this special address and a unique data value is termed an MSI vector.
Some adapter functions support only one MSI vector; other adapter functions support multiple MSI vectors. For functions that support multiple MSI vectors, the same special address is used with different data values.
In many computing platforms, a device driver configures itself as the interrupt handler associated with an MSI vector. This effectively associates an MSI vector with an entry in a CPU interruption vector. Therefore, when an adapter function supports multiple MSI vectors and is configured to use multiple MSI vectors, it consumes a corresponding number of entries in the CPU interruption vector.